The present disclosure relates to a bidirectional coupler. Wireless communication devices such as cellular phones include detector circuits to detect signal levels. For example, U.S. Patent Application Publication No. 2013/0293316 discloses a detector coupler capable of detecting signals transmitted on two different main lines by using a single sub-line.
In the configuration disclosed in U.S. Patent Application Publication No. 2013/0293316, a termination circuit is connected only on the output end side of the sub-line. Thus, it is possible to detect signals propagating from the input end side to the output end side of the main lines, whereas it is difficult to detect signals propagating from the output side to the input side. In the disclosed configuration, therefore, it is difficult to detect the level of, for example, a reflected signal obtained by reflecting a transmit signal from an antenna.